Are religion and religious differences to blame for war and conflict? Many war leaders have claimed to have God on their side, but should religion get the blame? A "War Audit" commissioned for the BBC programme "What the World Thinks of God" investigates the links between war and religion through the ages. It was carried out by researchers at the Department of Peace Studies at Bradford University.
George Bush was in little doubt about how the US-led coalition would bring down Saddam Hussein.
At a prayer meeting, shortly before the invasion of Iraq, he said: "Behind all of life and all of history, there's a dedication and purpose, set by the hand of a just and faithful God."
But God's help was being invoked in Baghdad, too. Saddam Hussein told Iraqis: "Fight as God ordered you to do."
So does that makes last year's Iraq conflict a religious war?
The authors of the War Audit suggest that it was arguably a war driven by religion.
But, as they point out, the Pope and the US Catholic bishops, the Archbishop of Canterbury and many theologians around the world argued that it fell well short of the rigorous criteria for a "just" war.
President Bush and Saddam Hussein were only the most recent of a long line of political leaders who have drawn on religion to help them in battle or to justify a military campaign.
But the War Audit set out to identify conflicts that were more closely linked to religious belief than to political causes - that could most properly be called religious wars.
And that, it concluded, means going back to the wars of Islamic expansion beginning in the 7th Century, the Crusades starting in the 11th Century and the Reformation wars beginning in the 16th Century.
Here the wars were fought primarily because of religious differences.
Most are much more complex.
To some extent, the nature of a war is in the eye of the beholder.
Osama Bin Laden portrays the campaign being waged by his terror network as a religious duty.
SELECTED EXTRACTS FROM RELIGIOUS TEXTS
'Then you must utterly destroy them; you shall make no covenant with them and show them no mercy' (Torah, Book of Deuteronomy 7:1-2)
'Thou shall not kill' (Torah, Book of Exodus 20:13)
'All who take the sword will perish by the sword' (New Testament, Matthew 5:43-44)
'Fight in the cause of God against those who fight you, but aggress not' (Koran 2:190)
'Whoever fights in the cause of God, then gets killed or attains victory, we will surely grant him a great recompense' (Koran 4:74)
'When all efforts to restore peace prove useless and no words avail, lawful is the flash of steel' (10th Sikh guru, Guru Gobind Singh)
'May your weapons be strong to drive away the attackers, may your arms be powerful enough to check the foes, let your army be glorious, not the evil-doer' (Hinduism's Rig Veda 1-39:2)
But the authors of the War Audit say it is much more about his opposition to the political order in Arab countries and the presence of US forces in Muslim nations.
One of the most extraordinary armed campaigns I have witnessed was that of the Holy Spirit Movement in Uganda in the 1980s, the forerunner of the Lord's Resistance Army that remains locked in battle with the Ugandan army in northern Uganda today.
Alice Lakwena, the leader of the Holy Spirit Movement, claimed that God had commanded her to seize the Ugandan capital and I and other journalists found and interviewed her in a banana grove about 100 kilometres (60 miles) short of Kampala.
Superstition played a large part in the progress her ragtag band of followers had made.
They smeared themselves with a potion they were told would protect them against the army's bullets.
But this bizarre campaign has also fed on northern political grievances in Uganda.
And this is echoed down the ages.
Few truly religious wars
The War Audit says that although armed conflicts may take on religious overtones, their genesis invariably lies in factors such as ethnicity, identity, power struggles, resources, inequality and oppression - and one factor is often exacerbated by another.
Why is religion a factor in war at all when all the main faiths have little time for violence and advocate peace?
It is often suggested that there has been a sharp rise in religiously motivated conflict.
But the authors of the War Audit say there have been very few genuinely religious wars in the past century.
The Israel-Arab wars from 1948 to the present day are often seen as wars over religion.
A Knight Templar from the time of the Crusades
In fact, they say, they have been about nationalism, self-defence or the liberation of territory.
So why is religion a factor in war at all when all the main faiths have little time for violence and advocate peace?
Because, it is suggested, leaders use differences over faith as a way of sowing hatred and mobilising support for political wars.
As the American civil war leader Abraham Lincoln put it almost 150 years ago: "The will of God prevails.
"In great contests, each party claims to act in accordance with the will of God. Both may be, but one must be wrong.
"God cannot be for and against the same thing at the same time."
What The World Thinks of God will be broadcast as follows: